Mice are any of the numerous small rodents of the family Muridae, especially of the genus Mus, introduced into the United States from Europe and now of wide distribution. While mice often live outdoors, they also establish themselves in human-occupied structures, such as houses, office buildings, etc. They can cause damage in such locations by chewing through walls, insulation, electrical wiring, etc. Mice also pose a health threat since they can transmit various diseases harmful to humans, especially through food contamination. Thus, most people find mice to be annoying and undesirable pests, and normally wish to exterminate them.
Mousetraps are well known devices used to catch, and usually to kill, mice. Such a trap is set in an open position, is baited with food attractive to mice, and is then left unattended. If a mouse comes along and attempts to take the bait, the trap will spring shut with the jaws thereof closing together on the mouse, thereby killing the mouse. The user will eventually find the mouse when checking the trap, can open the trap and dispose of the dead mouse, and can then reset the trap to catch another mouse.
One very common mousetrap has a rectangular wooden base with a U-shaped metal bail pivoted to the base between the ends thereof. A torsion spring normally urges the bail into a closed or sprung position in engagement with one end of the base. To set the trap, the user swings the bail against the force of the spring into engagement with the other end of the base, i.e. by rotating the bail approximately 180.degree. from its closed position. The bail is held in this set position by a catch that prevents the bail from closing. The trap includes a bait platform or trigger connected to the catch. When a mouse enters the trap and tries to take the bait, the catch is moved out of the way of the bail, and the bail snaps shut under the force of the torsion spring. The mouse is trapped between the bail and the base with enough force to kill it.
While traps of the type noted above are generally effective, they have a number of disadvantages. First, they can be tricky to set. The user has to swing and hold the bail down under tension while the catch is put in place. If this is not done properly, the bail can release accidentally, pinching the user's fingers. Moreover, the bail, when set, is under a constant spring force tending to close the bail. This puts stress on the components and will also unintentionally close the bail if the catch should slip slightly, thereby rendering the trap useless for its intended function. Finally, various eyelets or the like, or pivot rods, have to be used to pivotally mount the bail or other movable jaw component. These parts add complexity and expense to the trap.
U.S. Pat. No. 1,083,125 to Nebel discloses a mousetrap having a U-shaped pivotal bail bent to form pivot rod portions for pivotally journalling the bail in a rectangular base. A spring connects a lever arm attached to the bail to an outwardly extending support flange on the base. When the bail is placed in its open position to set the trap, the spring centerline is aligned with the support flange so that the spring does not exert a closing force on the bail. The trap includes an L-shaped trigger which pivots slightly when a mouse steps on it. The pivotal movement of the trigger pivots the bail to move the spring off dead center, thereby allowing the spring to become effective to snap the bail shut.
While Nebel discloses a mousetrap which is not constantly biased toward a closed position, it also has a number of disadvantages. It again requires the user to grab and rotate the bail, thereby putting the user's fingers at risk if he should let go before the bail is properly set, i.e. before the spring has reached the dead center position. In addition, the spring is external to the base, and is subject to being tampered with or accidentally jarred. This could cause the trap to be unintentionally tripped.